1. Field of the Invention
The present invention relates to an imaging apparatus that performs imaging of a specimen and acquires a digital image.
2. Description of the Related Art
An imaging apparatus that performs imaging of a microscope image such as a tissue slice of a human body and enables the accumulation and observation of digital image data has recently attracted much attention in the field of pathological diagnostic. In the imaging apparatus of this kind, a configuration (slide) in which a specimen, which is an observation object, is covered and fixed by a transparent protective member (cover glass) is typically used as a subject. When imaging of such a subject is performed, since the protective member is present between the specimen and an imaging optical system, the observed image is known to be degraded (decrease in contrast, blurring) due to optical aberration caused by the protective member. Further, the aberration is apparently caused not only by the protective member located on the slide. Thus, the aberration in the imaging optical system changes depending on ambient conditions such as temperature.
As a means for inhibiting the effect of aberration caused by the protective member, Japanese Patent Application laid-open No. 2011-095685 discloses a configuration in which a lens for spherical aberration correction is moved on the basis of focus information and structural information on a specimen acquired by pre-scanning, and a group of partial images acquired after the spherical aberration has been corrected are synthesized by image processing. Further, Japanese Patent Application laid-open No. 2008-276070 discloses a configuration in which an aberration correction amount is determined from the detected optical thickness of the specimen protective member and an image with corrected aberration is acquired by moving a correction ring mechanism.
Further, Japanese Patent Application laid-open No. H5-196873 discloses an objective lens having a structure that enables the user to attach an aberration correction lens as necessary.
Typically, there is an unpredictable spread in the thickness of the protective member of a specimen. Further, the aberration in the imaging optical system can change depending on ambient conditions such as temperature. Therefore, it is possible that optical aberration degrading the image quality changes among the slides or depending on the in-plane position in the same slide. Meanwhile, in hospitals, a large number of specimens should be observed by the aforementioned imaging apparatus to perform pathological diagnostic, and it is an important task to shorten the time needed to acquire image data on the specimen. However, the apparatuses described in the aforementioned Japanese Patent Application laid-open Nos. 2011-095685, 2008-276070, and H5-196873 are ineffective in acquiring images with corrected aberration with respect to each position when the correction amount differs depending on the position in the imaging region. This is because the correction of aberration is performed independently for each image of a subregion within the imaging region and it is necessary to synthesize thereafter the group of acquired images. When the correction amount differs depending on the position, the processing time is unavoidably increased. Accordingly, it is worthy of consideration to increase the speed by performing simultaneous imaging of a plurality of subregions, while correcting the aberration that differs depending on the position. Meanwhile, where the imaging is performed in one cycle, without dividing the imaging region into subregions, the accuracy of aberration correction (that is, image quality) will unavoidably spread depending on the position.